1. Field of the Invention
This invention relates generally to structural members, and more particularly to an open web Z-shaped metal structural beam capable of being nested and joined together in a lapped condition with like beams to form a continuous beam.
2. Brief Description of the Prior Art
The low-rise, commercial-industrial, retail building industry represents approximately two billion dollars in sales or about ten billion dollars of in-place cost yearly (1987 dollars). The conventional building construction industry currently relies primarily on the "bar joist" for use as a secondary simple span roof structural member in metal buildings. The "bar joist" is an open web structural configuration comprised of a top and bottom angle members connected by diagonal rod webs welded therebetween.
The metal building industry is a rival to the conventional construction industry and has been able to capture about 50 percent of the commercial-industrial building market or about 1 billion dollars in sales. The metal building industry currently relies primarily on a solid web "Z-purlin" as a secondary continuous span roof structural member in metal buildings, and combinations of other structural members such as metal main frames, girts, and thin walled metal sheeting to replace the conventional building structure. The Z-purlin is a solid web structural configuration comprised of a beam having a Z-shaped cross section having a top and bottom flange portion integrally connected by a solid flat web and are capable of being nested or overlapped. The laterally opposed longitudinal edges of the top and bottom flange portions may be inclined at an angle to form a stiffiner lip for increasing the strength of the flanges relative to the web portion.
Although the bar joist and Z-purlin are considered "secondary" members, they represent approximately 15 percent of the cost of the structurals in a building. There are several patents which disclose structural bar joist or Z-purlin members of various constructions.
Lowe, U.S. Pat. No. 4,461,134 discloses a Z-purlin beam formed or relatively thin roll-formed sheet metal having a generally Z-shaped cross section with a top and botton flange portion integrally connected by a solid flat web and has longitudinally extending or vertically spaced stiffening members at the juncture of the web and flange portions. The Lowe Z-purlin is capable of being nested or overlapped in inverted stacked relation for shipping. There is no suggestion of an open web.
Goeltz, U.S. Pat. No. 1,911,018 discloses an intertruss structural unit formed by welding iron or steel shapes or rods into interlaced truss members. Some of the basic strutural members which make up the primary and secondary trusses are open web configurations comprised of a top and bottom chord members connected rods welded therebetween. The chords are elongate longitudinal flanges, angles, or channels, and have various conventional cross sectional shapes, such as L-shapes, sideways Z-shapes, and T-shapes. The Goeltz structural members do not have a generally Z-shaped cross section and are not believed capable of being nested or overlapped, and there is no suggestion of providing a stiffener lip or edge on the chord members.
Thomson, U.S. Pat. No. 2,010,971 discloses a open web Z-stud beam formed of either sheet metal having a generally Z-shaped cross section with a top and bottom flange portion integrally connected by a slitted expanded web extending therebetween, or top and bottom L-shaped angle members connected rods welded therebetween.
Macomber, U.S. Pat. No. 2,457,250 discloses a tubular section generally open web structural joist member having a V-section top chord and a bottom chord formed of parallel tubular members with rods welded between the top and bottom chord members.
Smith, U.S. Pat. No. 3,670,471 discloses a sectional tower structure of triangular transverse section having detachable brace members on one side which can be stacked in nested relation when the braces along one side are detached.
The present invention is distinguished over the prior art in general, and these patents in particular by an open web metal structural beam having a generally Z-shaped transverse cross section and is capable of being nested and joined in a lapped position with like beam members. The beam has a top chord defined by an elongate longitudinal angle having an L-shaped transverse cross section, a bottom chord member defined by an elongate longitudinal angle having an L-shaped transverse cross section. The top and bottom chords are secured by an open web member in vertically opposed relation with the vertical leg portions of the L-shapes aligned vertically and the horizontal leg portions of the L-shapes in laterally opposed relation and the laterally opposed longitudinal edges of the horizontal leg portions of the L-shapes are bent to form vertically opposed longitudinally extending stiffener lips on the chord members. One or more metal angle members welded vertically between the vertical legs of L-shaped chord members on the side opposite the web increase the rigidity of the structural beam. The open web is formed of one or more metal bars secured at longitudinally spaced intervals between the vertical leg portions of the L-shaped top and bottom chord members in a longitudinally extending diagonal configuration extending between the top and bottom chords. The Z-shaped beams may be nested for shipping and joined together to span greater distances than the single beams alone.